Calendar of Physics Talks Vienna

Quantum sensing and simulation with light

Speaker:

Jake TAYLOR (JQI/NIST)

Abstract:

Advances in quantum optics in novel domains — such as with superconducting circuits or mechanical oscillators — lead to intriguing new possibilities for observing and controlling quantum behavior in increasingly large systems. In this talk, I consider how we can use optomechanical and circuit QED systems for quantum-limited measurement and transduction of forces and fields. Furthermore, I will develop a set of techniques to take these systems into the regime of quantum simulation, with the goal of showing theoretically that all the necessary tools for observing the fractional quantum Hall effect for light are in place, from a robust, effective chemical potential for light to strong two-photon interactions to synthetic magnetic fields for photons using linear or parametric optical elements.

Date:

Mon, 19.05.2014

Time:

11:00

Duration:

60 min

Location:

Atominstitut, Hörsaal, Stadionallee 2, 1020 Wien

Contact:

Peter Rabl

Big Data of Materials Science from First Principles -- Critical Next Steps

Using first-principles electronic-structure codes, a huge number of materials has been studied in recent years. The amount of already created data is immense. Thus, the field is facing the challenges of “Big Data”, which are often characterized in terms of the “four V”: Volume (amount of information), Variety (heterogeneity of the form and meaning of the data), Veracity (uncertainty of the data quality), and Velocity at which data may change or new data arrive.
Obviously, the computed data may be used as is: query and read out what was stored. However, for achieving deeper and novel scientific insight, the four V should be complemented by an “A”, the Big-Data Analysis. Calculating properties and functions for many materials, (e.g. efficiency of potential photovoltaic, thermoelectric, battery, or catalytic materials) is the necessary first step. Finding the actuating mechanisms (the “causes”) of a certain function is the desired science. In fact, such scientific understanding is needed for deciding what new materials should be studied next as most promising novel candidates and for identifying interesting anomalies.
For many, maybe most, material functions, the “cause → property/function” relation is complex and indirect. Let us label the “cause” by a multi-dimensional descriptor d, which is initially unknown. The property/function is a number P (e.g. the thermoelectric figure of merit of a material), or a string of numbers. From statistical-learning theory, it is known that inverting the d → P mapping, i.e. identifying the cause from known data P, is an ill-posed problem, even when a one-to-one correspondence exists: A little error in the data P may suggest a very different cause d.
From the above-mentioned issues, the 4V & A, and for first-principles computational materials science and engineering, the two key challenges concern big-data veracity and analysis. These are at the focus of this talk.

Surface reactions can be followed in detail using X-ray photoelectron spectros¬copy (XPS or ESCA). From the binding energies of the adsorbate and sub¬strate core levels, detailed information on the chemical composition, chemical state (e.g. oxidation state), adsorption sites, but also on the photoemission process itself can be derived. Different examples will be addressed in this presentation. The first example deals with the oxidation of sulphur on stepped platinum surfaces. The second example deals with the characterization and modification of the surface properties of ionic liquids (ILs). Due to their low vapor pressure, the full arsenal of UHV-based surface scien¬ce methods can be applied to investigate this material class and detai¬led information can be derived. Particular emphasis will be given on the composition of the IL/vacuum interface, the properties of ultrathin IL layers on

The most recent generation of cold atom experiments uses atoms in Rydberg states to explore many-body phenomena. In this talk I will focus on the non-equilibrium dynamics of such systems where non-trivial behavior is generated by the competition between coherent laser excitation, dissipation and the strong interaction between Rydberg atoms. I will discuss the relaxation of Rydberg lattice gases, showing that it is hierarchical and strongly correlated. This establishes a connection to kinetically constrained systems that are used in soft condensed matter physics as models for the description of glassy phenomena.

Quantum entanglement and typicality play a crucial role to understand the foundations of statistical mechanics. Recently, it has been suggested than the former is also relevant to explain the connectedness of spacetime. In particular, a direct relation between semiclassical wormholes and quantum entanglement has been conjectured. In this talk, I will first discuss some necessary, but not sufficient, conditions that correlation functions of low energy gravity probe operators must satisfy to allow an interpretation in terms of a semiclassical wormhole. I will then study typicality of these correlators in the space of quantum states having the same amount of entanglement. To compute these correlators I will argue that low energy gravity probe operators behave like random matrices when acting on the space of black hole microstates. I will conclude that typical entangled states do not allow a semiclassical wormhole interpretation.

Electromagnetically induced transparency (EIT) incooperating a long-lived Rydberg state can result in collective optical nonlinearities mediated by the long-range interaction between Rydberg atoms, which enables manipulation of light fields on the single photon level. Recent experimental results based on this novel approach include efficient single photon generation, demonstration of attractive interactions between photons, and efficient all-optical switching.
Here we present our realization of an all-optical transistor based on the mapping of gate and source photons into strongly interacting Rydberg
excitations with different principal quantum numbers in an ultracold atomic ensemble. We obtain a record switch contrast of 40 % for a coherent gate input with mean photon number one and demonstrate attenuation of source transmission by over 10 photons with a single gate photon.

Date:

Fri, 23.05.2014

Time:

10:30

Duration:

90 min

Location:

Hörsaal Atominstitut, Stadionallee, Wien 2

Contact:

Peter Rabl

String Cosmology

Speaker:

Timm Wrase (Stanford U.)

Abstract:

I give a brief introduction to string cosmology. Then I review the results of the BICEP2 experiment that recently
discovered B-mode polarization. Interpreting these B-modes as primordial gravitational waves gives strong evidence for
cosmic inflation at roughly the GUT scale. This discovery is not only a smoking gun for inflation but also provides us
with access to physics near the GUT scale. I describe new ways of obtaining inflation in string theory that lead to
predictions that match the new measurements by BICEP2. Lastly, I mention some on-going work on constructing new large
classes of dS vacua in supergravity and string theory.

The phase transition and jet quenching parameter have been investigated in the framework
of dynamical holographic QCD model. It is found that both the trace anomaly and the ratio
of the jet quenching parameter over cubic temperature show a peak around the critical temperature,
and the ratio of jet quenching parameter over entropy density sharply rises at Tc.
This indicates that the jet quenching parameter can characterize the phase transition. The effect
of jet quenching parameter enhancement around phase transition on nuclear modification factor and
elliptic flow have also been analyzed, and it is found that the temperature dependent jet quenching
parameter from dynamical holographic QCD model can considerably improve the description of jet
quenching azimuthal anisotropy as compared with the conformal case.